1. Field of the Invention
The present invention generally relates to the art of thin layer chromatography. Particularly, it is concerned with conversion of a conventional chromatographic plate into a reverse-phase chromatographic plate and a method for preparing the plates.
It is widely known that reverse-phase chromatography is useful in separating polar and/or labile compounds which are difficult to separate by a normal-phase chromatography.
In general, the art of reverse-phase chromatography is useful in separation or identification of natural substances or synthetic organic compounds such as steroid hormones, vitamins, naturally occuring or semi-synthetic antibiotics or synthetic bactericidal agents. A thin layer chromatographic plate can also be used for prefixing conditions under which conventional column chromatography or high performance liquid chromatography of the reverse phase system could be performed.
In order to properly perform reverse-phase thin layer chromatography, it is essential to intentionally reduce the chromatographic activity of the adsorbent to the limit of ascending the solvent for development. Namely, a satisfactory adsorbent activity should be maintained to an extent such that the developing solvent can naturally ascend at least 10 cm from the spotted line, because pressure cannot be exerted on the mobile phase.
2. Description of the Prior Art
An alkylsilylated adsorbent, silica gel having monomethylsilyoxy, dimethylsilyloxy, octylsilyloxy or dodecylsilyloxy group is known, and, at first sight, there seems to be no obstacle in obtaining a plate for reverse phase thin layer chromatography by forming a layer with one of these adsorbents. The actual preparative procedure is, however, not necessarily easy, and the obtained plates are not always satisfactory in many respects as will be elucidated hereinbelow in the Description of the Preferred Embodiments as comparative preparations.
In addition to this, uniform alkylsilylation of the entire surface of the metal oxide adsorbent layer for the intended purpose, while retaining its ascending tendency to an acceptable extent, is not always possible by a conventional method wherein the layer is simply contacted with an alkylsilylating agent such as alkylchlorosilane.